Weight gain with balanced diet and question about food allergies

My daughter is allergic to milk, eggs, and soy. I am allergic to peanuts, and she has not had peanuts in several years. Is it possible for her to develop an allergy? I am afraid for her to eat peanuts. Also, how can she get her nutrients with all of these allergies?  She is not able to do much during the day because she is working on school. I am worried that she is not getting proper nutrients due to her food allergies. Also, is it normal to gain weight after just eating 1200 calories a day? My daughter eats very healthy. She only drinks water, and eats lots of fruits and veggies. However, she is still gaining weight even at just 1200 calories. She increased physical activity with higher calories, but still gained weight, so she lowered her calories. Why could this be? She exercises on the treadmill 3-4 times a week.. Is that enough physical activity? She also dances. She is not able to do any physical activity during the day due to her school work. She is not typically a snacker. If she has a snack she may have celery with almond butter. How many calories should she be eating?

[Renee Radenberg]

Her weight is the 10-5th percentile for her age which indicates she is in the low normal range for her age. She is in puberty and women gain weight during that time. She should not lower her calorie intake because she is still growing and the body needs the calories to grow. For her age, she needs 1800-2000 calories per day. It is good she is eating healthy. Suggest going to an Allergist to see if she is allergic to peanuts or not. If she is eating almonds, then more than likely she is not, however, it is best to get her tested. Suggest a daily multi-vitamin with iron to insure she is getting the proper amount of vitamins and minerals due to her allergies. Hoped this helped you.